The present invention relates to the field of linear motors, and in particular to linear motors having a covered secondary.
In general, a linear motor includes a, normally fixed, secondary or reactive part, having in case of a synchronous linear motor a plurality of magnetic elements (permanent magnets) arranged side-by-side to define a guideway for a rotor which is movable relative thereto and represents the primary of the linear motor. The rotor interacts with the magnets of the secondary and converts this interaction into a translatory motion.
Such linear motors are used as drives in various technological fields, for example, in machine tools, machining devices such as automatic drills, automatic milling cutters, automatic lathes, automatic placement machines or automatic bonding machines, including vehicle drives in magnetic levitation trains, etc.
In particular, when the linear motor is exposed to rough operating conditions, the secondary is covered for protection from dust, operating liquid, aggressive substances or chips. German patent publication no. DE 198 53 250 describes a cover for a secondary of an electric linear motor. The cover is made of low ferromagnetic material and is held by magnetic force on the secondary, which carries permanent magnets. Although the secondary is protected from dropping material, there is still the problem that material remains on the cover and may migrate into the air gap between the primary and the secondary.
It would therefore be desirable and advantageous to provide an improved secondary to obviate prior art shortcomings and to allow replacement and/or cleaning of a cover in a simple manner.